This invention relates to a receiving material for electrophotographic toner and, more particularly, to such a material on which can be formed an image of high photographic quality that has substantially uniform gloss in the entire image area and to a method for making such materials.
In electrophotographic copying and laser printing, an electrostatic latent image is formed on a photoconductive surface and, for dry development, is then contacted with dry electrostatically charged toner particles which comprise a thermoplastic binder polymer and a pigment. The resulting pattern of toner particles is then transferred, usually by electrostatic attraction, to a receiving material, e.g., a sheet or web of paper, to which the toner is fixed by heat and pressure, e.g., by passage through the nip of heated fuser rolls or a fuser belt, thus forming an electrophotographic toner image on the receiving material. This widely used office technology is quite successful in forming black-and-white copies of documents, using paper sheets as the receiving material. The known procedures, however, are not entirely successful in forming images that have the high quality of continuous tone images formed by conventional silver halide photography. In particular, electrophotographic prints or copies of such images on paper have lacked the uniform gloss and the feel of prints made by conventional photography. The present invention provides a novel receiving material for electrophotographic toner and a method for making such material. With the novel receiver material, continuous tone images of high quality and substantially uniform gloss in the entire image area can now be obtained by electrophotography.
Although receiver sheets for electrophotographic toners are most often paper, an untreated paper surface is usually too rough to give a toner transfer image of high resolution. A particularly serious disadvantage of a paper receiver sheet is that, being fibrous and hydrophilic, it unavoidably contains moisture. Accordingly, when heated in the toner fusing step, the moisture in the paper vaporizes and causes buckling and distortion of the toned image, especially in large areas of toner. In addition, a paper receiving sheet is susceptible upon exposure to water to distortion, tearing and other damage.
A need exists for an improved paper toner receiver sheet, especially for forming glossy continuous tone or half-tone images of high quality and uniform gloss. Such a sheet should be resistant to water absorption and capable of forming images with large toner areas that will not crack as a result of deformation of the paper resulting from water absorption. The paper should not curl or wrinkle. The present invention provides a novel paper receiving sheet for toner images, including continuous tone color images formed by extremely small dry toner particles, that overcome the problems of prior art toner receiving materials.
The invention provides a novel receiving material for thermoplastic, electrophotographic toners having glass transition temperature or Tg in the range from about 45xc2x0 C. to 60xc2x0 C. and comprises (a) a paper support, (b) a hold-out layer comprising a water-resistant, thermoplastic polymer coated on said support, and (c) a toner receiving layer coated on said hold-out layer. In the novel receiving material, the receiving layer comprises a thermoplastic polymer that is coatable from an aqueous medium, has a Tg within 5xc2x0 C. of the Tg of the toner polymer and is adhesively compatible therewith. The receiving layer when coated and dried on said hold-out layer has a 60xc2x0 gloss of at least about 60 and not substantially less than the gloss of the toner when the toner is fused and adhered to the receiving layer. The support, toner-receiving layer and conductive hold-out layer together have a volume resistivity in the range of 1.0xc3x97108 to 1.0xc3x971013 ohm-cm.
The invention further provides a method of making a receiving material for electrostatically charged thermoplastic toner. The method comprises forming on an opaque reflective paper support a smooth, water-impermeable, hold-out layer of a thermoplastic polymer, forming a toner-receiving layer by coating on said hold-out layer an aqueous dispersion of a thermoplastic polymer that is adhesively compatible with the polymer of said hold-out layer and adhesively compatible with said toner. The polymer of said toner-receiving layer has a Tg within 5xc2x0 C. of the Tg of said thermoplastic toner. The toner receiving layer when coated and dried has a 60xc2x0 gloss of at least 60 and not substantially less than the gloss of said toner when adhered to the receiving layer. The support, toner-receiving layer and conductive hold-out layer together have a volume resistivity in the range of 1.0xc3x97108 to 1.0xc3x971013 ohm-cm.
The invention still further provides a method of forming an electrophotographic image, employing the novel toner receiving material.